Syscalls: Make system calls access arguments like a stack, not an array.

When accessing arguments for a syscall, the position of an argument depends on
the policies of the ISA, how much space preceding arguments took up, and the
"alignment" of the index for this particular argument into the number of
possible storate locations. This change adjusts getSyscallArg to take its
index parameter by reference instead of value and to adjust it to point to the
possible location of the next argument on the stack, basically just after the
current one. This way, the rules for the new argument can be applied locally
without knowing about other arguments since those have already been taken into
account implicitly.

All system calls have also been changed to reflect the new interface. In a
number of cases this made the implementation clearer since it encourages
arguments to be collected in one place in order and then used as necessary
later, as opposed to scattering them throughout the function or using them in
place in long expressions. It also discourages using getSyscallArg over and
over to retrieve the same value when a temporary would do the job.

3 files changed, 15 insertions, 10 deletions

diff --git a/src/arch/mips/linux/process.cc b/src/arch/mips/linux/process.cc
index dde3a4efd..c2a05b73b 100644
--- a/src/arch/mips/linux/process.cc
+++ b/src/arch/mips/linux/process.cc
@@ -51,7 +51,8 @@ static SyscallReturn
 unameFunc(SyscallDesc *desc, int callnum, LiveProcess *process,
           ThreadContext *tc)
 {
-    TypedBufferArg<Linux::utsname> name(process->getSyscallArg(tc, 0));
+    int index = 0;
+    TypedBufferArg<Linux::utsname> name(process->getSyscallArg(tc, index));
 
     strcpy(name->sysname, "Linux");
     strcpy(name->nodename,"m5.eecs.umich.edu");
@@ -70,14 +71,16 @@ static SyscallReturn
 sys_getsysinfoFunc(SyscallDesc *desc, int callnum, LiveProcess *process,
                    ThreadContext *tc)
 {
-    unsigned op = process->getSyscallArg(tc, 0);
-    // unsigned nbytes = process->getSyscallArg(tc, 2);
+    int index = 0;
+    unsigned op = process->getSyscallArg(tc, index);
+    unsigned bufPtr = process->getSyscallArg(tc, index);
+    // unsigned nbytes = process->getSyscallArg(tc, index);
 
     switch (op) {
       case 45:
         { 
             // GSI_IEEE_FP_CONTROL
-            TypedBufferArg<uint64_t> fpcr(process->getSyscallArg(tc, 1));
+            TypedBufferArg<uint64_t> fpcr(bufPtr);
             // I don't think this exactly matches the HW FPCR
             *fpcr = 0;
             fpcr.copyOut(tc->getMemPort());
@@ -97,15 +100,17 @@ static SyscallReturn
 sys_setsysinfoFunc(SyscallDesc *desc, int callnum, LiveProcess *process,
                    ThreadContext *tc)
 {
-    unsigned op = process->getSyscallArg(tc, 0);
-    // unsigned nbytes = process->getSyscallArg(tc, 2);
+    int index = 0;
+    unsigned op = process->getSyscallArg(tc, index);
+    Addr bufPtr = process->getSyscallArg(tc, index);
+    // unsigned nbytes = process->getSyscallArg(tc, index);
 
     switch (op) {
 
       case 14:
         {
             // SSI_IEEE_FP_CONTROL
-            TypedBufferArg<uint64_t> fpcr(process->getSyscallArg(tc, 1));
+            TypedBufferArg<uint64_t> fpcr(bufPtr);
             // I don't think this exactly matches the HW FPCR
             fpcr.copyIn(tc->getMemPort());
             DPRINTFR(SyscallVerbose, "sys_setsysinfo(SSI_IEEE_FP_CONTROL): "
diff --git a/src/arch/mips/process.cc b/src/arch/mips/process.cc
index b9f608922..d96b0c81c 100644
--- a/src/arch/mips/process.cc
+++ b/src/arch/mips/process.cc
@@ -147,10 +147,10 @@ MipsLiveProcess::argsInit(int intSize, int pageSize)
 
 
 MipsISA::IntReg
-MipsLiveProcess::getSyscallArg(ThreadContext *tc, int i)
+MipsLiveProcess::getSyscallArg(ThreadContext *tc, int &i)
 {
     assert(i < 6);
-    return tc->readIntReg(FirstArgumentReg + i);
+    return tc->readIntReg(FirstArgumentReg + i++);
 }
 
 void
diff --git a/src/arch/mips/process.hh b/src/arch/mips/process.hh
index b8f4de20a..f35ec8554 100644
--- a/src/arch/mips/process.hh
+++ b/src/arch/mips/process.hh
@@ -50,7 +50,7 @@ class MipsLiveProcess : public LiveProcess
     void argsInit(int intSize, int pageSize);
 
   public:
-    MipsISA::IntReg getSyscallArg(ThreadContext *tc, int i);
+    MipsISA::IntReg getSyscallArg(ThreadContext *tc, int &i);
     void setSyscallArg(ThreadContext *tc, int i, MipsISA::IntReg val);
     void setSyscallReturn(ThreadContext *tc, SyscallReturn return_value);
 };